Fossil Lake was the smallest and shortest-lived of the Green River System lakes. At its largest size, the lake covered 932 square miles and existed for approximately three million years. One phenomenon of the Fossil Lake fossils is their density. There are as many as several hundred fossilized fish per square meter in some portions of Fossil Butte. At least thirteen genera of fish are found in the sediments of Fossil Lake, as well as a wide variety of species, from large predators like gar and bowfin to the now extinct Knightia, Diplomystus, and Priscacara. Plant and invertebrate records are equally diverse. Evidence of lily pads, horsetails, ferns, palms, and poplar and elm trees exists along Fossil Lake’s floodplain and lower elevations. The remains of dragonflies, mosquito larvae, and water striders bear testament to the vibrancy of this freshwater ecosystem. In addition, evidence of freshwater mollusks, snails, crayfish, and shrimp has been found.

The paleontologists who worked at Fossil Butte have deposited specimens at the Field Museum in Chicago, IL, the American Museum of Natural History in New York City, and Smithsonian Institution’s National Museum of Natural Hostory in Washington, D.C.

OTHER TIDBITS: That pretty well sums it up!

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Annotations:
It’s actually about 7 miles east of Fossil Butte National Monument and 5.8 miles west of Kemmerer on the north side of Highway 30!

From Casper: ~292mi (470km) — 4.9hrs
From Cheyenne: ~345mi (556km) — 5.8hrs
From Evanston: ~54mi (87km) — 0.9hrs
From Jackson: ~165mi (266km) — 2.8hrs